1. Field of the Invention
This invention relates to a bedside apparatus and method for the collecting, measuring and monitoring of the output volume of liquids, especially urine and CSF, drained from a catheterized patient, at specific medical conditions, by means of an optical refraction method with an option to monitor also pressure from the drained organ and to correlate it to the drained volume, and to a computer readable media containing programmed instructions for carrying out the steps of the method.
2. Prior Art
The importance of monitoring discharged body fluid's volume level has long been known to the medical profession. For example, low urine output in critically ill patients can be an early sign of deteriorating patient condition as a result of renal failure, high intra-abdominal pressure, or congestive heart failure even before changes in other vital signs, such as, blood pressure, temperature, pulse and respiration are observed. In addition, for a critically ill patient, changes in hemodynamic measurement of cardiac output such as arterial blood pressure, central venous pressure and left arterial pressure are meaningless, if these changes are not correlated with changes in the perfusion of major organs, such as, the kidney.
In addition to urine drainage measurement, the bladder pressure measurement can give good indication of the intra-abdominal pressure. High intra-abdominal pressure (IAP) occurs frequently in patients with acute abdominal syndromes, such as, ileus, intestinal perforation, peritonitis, acute pancreatitis or trauma. An elevated IAP may lead to intra-abdominal hypertension (IAH) and abdominal compartment syndrome (ACS). Both IAH and ACS are etiologically related to an increased morbidity and mortality of critically ill patients.
The increase of the volume within the elastic structure of the abdominal wall causes an increase of overall pressure in the cavity and organs, and it may decrease tissue blood perfusion. An increase in abdominal pressure may lead to distant effects in other parts of the body, such as increased intracranial pressure, pericardial tamponade and tension pneumothorax or extremity compartment syndrome.
Monitoring Inner Cranial Pressure (ICP) and CSF are also of vital importance due to the dangerous nature of an increase in the ICP of a patient. The cranium is a rigid container, and an increase in any of its contents—brain, blood, or CSF—will increase the ICP. In addition, any increase in one of the components must be at the expense of the other two; this relationship is known as the Monro-Kellie doctrine. Injury to the brain occurs both at the time of the initial trauma and subsequently due to ongoing cerebral ischemia. In an intensive care unit, raised intracranial pressure (intracranial hypertension) is seen frequently after a severe diffuse brain injury (one that occurs over a widespread area) and leads to cerebral ischemia by compromising cerebral perfusion.
Cerebral perfusion pressure (CPP), the pressure causing blood flow to the brain, is normally fairly constant due to auto regulation, cerebral perfusion pressure is calculated by subtracting the intracranial pressure from the mean arterial pressure: CPP=MAP−ICP. One of the main dangers of increased ICP is that it can cause ischemia by decreasing CPP. Once the ICP approaches the level of the mean systemic pressure, it becomes more and more difficult to squeeze blood into the intracranial space. As an intracranial mass lesion or oedematous brain expands, some compensation is possible as cerebrospinal fluid (CSF) and blood move into the spinal canal and extra cranial vasculature, respectively. Beyond this point, further compensation is impossible, ICP rises dramatically and only external removal of CSF can lower the ICP level.
Monitoring of CSF & Urine Output
Urine output is being measured manually by means of various measuring collecting systems. Such systems normally contains a collecting and measuring rigid transparent vessel hanged by the bedside to allow gravitational drainage, having a graduated scale and an inlet tube connected to a catheter. The measuring rigid transparent vessel has an emptying valve being connected to a secondary elastic reservoir. The liquid output volume is measured and then emptied to the secondary reservoir at predetermined hourly intervals. The above volume metering procedure also enables to visualize during the measurement intervals the optical visualized properties of the drained urine, such as, color, turbidity and possible sedimentation which gives more clinical information.
Manually Measurement of intra-abdominal pressure on a catheterized patient using the bladder is done by injecting a known quantity of saline through the Foley catheter into the bladder, then closing the drainage and measuring the pressure inside the bladder by means of pressure transducer.
Intracranial pressure is manually measured with the use of pressure transducers. A catheter is surgically inserted into one of the brain's lateral ventricles and is used to drain CSF (cerebrospinal fluid) in order to decrease ICP's. This type of drain is known as an EVD (extra ventricular drain). The CSF is drained into a rigid transparent vessel in the same manner as described above, but instead of using a gravitational drainage approach, a liquid column gauge procedure is used where the CSF drainage will be depended on the water column height, which is defined by the height of the rigid container. This drainage, as in the urine volume metering system, enables to visualize during the measurement intervals the CSF color, turbidity and possible sedimentation which provides more clinical information.
Different designs of collecting vessel, which differ in their collecting volume capacity and accuracy, are used for a variety of procedures in different hospital wards. For instance, for pediatric urine measurement a small rigid container is needed as opposed for adults where a larger container is required. Also, for intensive care units and operating rooms the accuracy of the urine drainage measurement has to be substantially higher than in other wards, therefore, the urine collecting vessel used is require to have a higher degree of accuracy. In the case of CSF drainage a small and precise collecting vessel is required.
Clinicians have been searching for a methodology for the automatic collection and data analysis of fluids outputs like Urine and Cerebrospinal-fluids (CSF) in real time. Manual procedures require measurement of contained volume by the end of a preselected time interval, thus consuming costly nursing time, and in addition risking the accuracy of the measurement due to inaccurate scale reading and non-precise following of the preselected time interval. Another factor relates to the increased risk of cross contamination due to the frequent manual operation of the system. In addition, all liquid output results are recorded manually and cannot be transferred automatically to a ward computer network unless the observed data is typed-in.
All of the above are some of the main reasons for the desirability of more accurate online electronic liquids output measuring and monitoring systems.
Electronic meters for monitoring urine output of a patient are well known and feature different measuring techniques. An ultrasonic measuring technique is shown in U.S. Pat. No. 4,448,205, U.S. Pat. No. 4,658,834, U.S. Pat. No. 5,891,051 and U.S. Pat. No. 6,582,379. In the ultrasonic systems described, the patient fluid is discharged into a container with an ultrasound transducer mounted to a housing adjacent the container and acoustically coupled to a wall of the container. When a sound wave hits the interface between the air and the liquid in the container, the signal is reflected. The measurement of the volume is being done by determining the time duration required for the transmitted energy to travel from the transducer to the upper surface of the collecting urine pool and back again.
Drawbacks of these types of measurements techniques are due to the sensitivity of the measurement. Tilting of the measuring vessel, particles such as blood in the liquid, foam and temperature changes of the liquid can all cause inaccurate readings? In addition there is a great need for transducer calibration and there might be risk of ultrasonic interference with other ultrasonic measuring devices. There is also accumulation of the drained urine without the possibility of being able to measure new fresh specimens of urine according to predetermined time intervals or desired volume quantity. As a result of this drained fluid accumulation, it is not possible to view the optical properties of the freshly drain urine which can provide additional important information.
Use of a method of weighing the body of drained fluid mass with a force transducer/weight cell is described in patents DE 3544676, EP 0242128B1, U.S. Pat. No. 5,769,087 and U.S. Pat. No. 5,776,077, where the accumulated body fluid is suspended from the force transducer/weight cell. This measurement is very much effected by the movement of the measured bag and the inclination of the bag from its horizontal state, which can easily lead to hardly detectable false measurements. Moreover, as mentioned above, the measured liquids are being accumulated with no ability to view the optical properties of fresh urine output specimens.
Using a drops counting method is described in EP 0901778A2 and U.S. Pat. No. 6,640,649B1, and requires having a drip chamber with a sensor that includes a light source located on one side of the chamber and a light detector located on the opposite side of the chamber. The system preferably includes a filter upstream of the drip outlet and some type of restriction, “drop generating orifice”, to enable to “create a standard drop”. The main problem with this type of method is the fact that the drained fluid can be viscose and may include foreign objects and sedimentation, which can lead to occluded filters and a blocked drop generation orifice. Furthermore, with this method, as well as with the ones mentioned above, it is not possible to view the optical properties of freshly drained urine, which can provide additional important information.
In addition to the above methods there are also optical methods, such as the one described in the U.S. Pat. No. 4,343,516. As described, there is a chamber of specific configuration having two electronic controlled valves located above and below the chamber and an optical sensor situated at the top of the chamber below the upper valve. The lower valve is closed when urine enters the chamber until the point where the urine level reaches the optical sensor at which time, by virtue of electronic control, the upper valve will close and the lower valve will open, allowing the urine to pass into a collection receptacle drainage bag. These methods have the drawback that the measurement is related to the chamber volume, so until the chamber is filled there is no possibility to know the amount of drained urine. The volume range of the chamber is usually between 5-10 cubic centimeters. In case of movement of the chamber the urine can accidently reach the optical sensor and the lower valve will be opened and the measurement will not be accurate. For the visualizing of the optical properties 10 cubic cm could be a too small volume and the “turnover” of the urine might be too fast.
Another optical method is described in U.S. Pat. No. 4,745,929. In this method, the drainage system comprises a container having a rigid conduit to receive the liquid and a receptacle to receive the urine after its accumulation in the conduit. The filling and empting of the conduit is done as in the previously described optical method, but in this method the height of the liquid in the conduit is measured. This measurement is done by using a pair of emitters (LEDs) and detectors, where the level of the liquid is detected by means of refraction. The main drawback of this method is the fact that there is no possibility to measure the liquid level when it lays in-between the pair of LEDs.
Automatic measurement of ICP & CSF can be seen in the German patent EP 174954981. In this system the CSF is pumped out in accordance to the ICP measurement. The problems with this method are, risk of accidental over pumping and that the fact that the CSF cannot be visualized, since it is drained into one container after the peristaltic pump. In addition, the measurement of the amount of CSF is calculated from the number of turns of the peristaltic pump, according to the tubing size used, which leads to inaccurate readings due to changes in the tube.